1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus for use in a copying machine, a laser beam printer, or the like.
2. Description of the Related Art
In recent years, this type of device is popular among personal users, and a smaller device produced at lower cost is required for satisfying personal user's needs.
In using such a small-sized apparatus, generally designed as a desk-top type, the user prefers to change its position or direction freely on the desk. The user wishes to make effective use of a limited desk space and to use the space in his or her own style. Therefore, it is desirable that the apparatus can be set in various attitudes by using the side or top planes of the body alternatively as a bottom supporting the apparatus body.
However, a conventional image forming apparatus is generally large-sized, and when placing the apparatus on a desk or the like, the plane to be the bottom is predetermined. Accordingly, the apparatus has to be placed in one specific attitude. Therefore, in designing the structure of the developing device or positional arrangement of various elements in the body, the possibility of the apparatus being used in various attitudes is not taken into consideration.
If placing the apparatus using different planes as a bottom, the apparatus body is turned in various directions. The positional relationship among elements provided in the body and the direction of gravity influence vary in accordance with the change of placement direction, whereby the stream of the moving developer and air flow change in the apparatus body. As a result, the following problems occur.
First, as for positional relationship among the elements, the elements located above a fixing device are heated by the air rising from the fixing device, which is a large heat source. This causes heat deformity and a change of characteristics in the elements.
Secondly, in the case of using a laser scanner as an exposure means, due to the change of placement attitude of the body, the shaft of the motor for revolving the mirror used in the laser scanner may be slightly shifted from its proper position by the influence of gravity. As a result, the accuracy of scanning by laser light is reduced, and then the quality of the developed image is degraded.
Further, in the developing device, the state of supplying developer changes depending on the gravity effect varying due to the change of the direction of supplying the developer to a photosensitive body. In such a state, an excessive supply of developer may cause the developer to clog or high density condition similar to this, which applies an extreme stress on the developer. Conversely, the amount of supplied developer may be insufficient.
Furthermore, if the attitude of the developing device itself is changed, the developer particles gather in the lower side in the developing device. Also, there is a need to forward and transport the developer against the gravity effect. These difficulties prevent the developer from being supplied uniformly to every portion of the developing section on the photosensitive body. Because of this, the stability of the developing performance is reduced.